Australian Prime Minister Julia Gillard and opposition leader Tony Abbott spent the last sitting day for the year locked in a verbal battle on the floor of Parliament over the Australian Workers’ Union affair.

The confrontation followed the Prime Minister’s call to suspend question time, demanding the Opposition Leader back up his claims that she broke Western Australian laws in her dealings with her former boyfriend’s alleged fraud. Glaring at Abbott, the Prime Minister told him to substantiate his claims or offer an unreserved apology.

The Opposition quickly agreed to the suspension, with Abbott and Gillard given 15 minutes each to argue their case.

Addressing the House of Representatives, the opposition leader called for a judicial inquiry into the Prime Minister’s conduct, though was careful not to directly accuse her of committing a crime, as he had earlier on Thursday morning.

"Plainly there has been illegal and unethical conduct here," Abbott said. "Much of it has been facilitated at the very least by the Prime Minister and the advice she has given".

Speaking under parliamentary privilege, Abbott said Gillard was a "dodgy and unethical lawyer" and "an untrustworthy Prime Minister".

He accused her of misleading Parliament on the matter five times in the past week, when asked.

Gillard spent her time during Abbott’s 15 minutes, looking closely at the opposition leader and writing notes.

A newly released document confirms that Gillard, then a solicitor at Slater & Gordon, wrote to the WA Corporate Affairs Commission in mid-1992 rejecting the commission’s assertion that the Australian Workplace Reform Association was ineligible for incorporation because of its trade union status.

In the House this afternoon, Gillard attacked Abbott for "overreaching" when he had accused her of a crime.

Calling his parliamentary speech halting and nervous, she said the opposition leader had no evidence to support his earlier claims that she "made false representations" and "must have known of wrongdoing".

"He had had an opportunity today to put up and he has not been able to do so," Gillard said.

"A decent man would apologise. A decent man would recognise that he has gone too far, that he has made an error, that he has relied on a false report. If the leader of the opposition was a decent man he would have used his 15 minutes to say ... he was wrong."Despite the half-hour debate, when question time resumed, it was still dominated by the AWU affair.

Abbott and deputy opposition leader Julie Bishop continued to press Gillard over her conduct as a lawyer.

The Prime Minister continued to argue she had done nothing wrong.

''It is ridiculous,'' she said of the Coalition attack.

The Prime Minister’s office released a statement earlier on Thursday, saying "so what?" to reports that Gillard wrote to the West Australian Corporate Affairs Commission in 1992.

A spokesperson for Gillard called on the Liberal Party to give up its "witch hunt" against the Prime Minister, saying she just did "what lawyers do" as a lawyer at Slater & Gordon in the 1990s.

"So, the Prime Minister wrote to the WA Commissioner? So what? She did what lawyers do. Act on instruction. Provide legal advice," the spokesperson said.

"What does the transcript show? That the PM said the association wasn’t a union. So what? It wasn’t a union ...

"The Prime Minister has not done anything wrong. No evidence has been produced that she did anything wrong."

Ms Gillard has also written to Fairfax chief Greg Hywood claiming reports in Fairfax papers today were misleading and declaring that the new document supported her account that she had nothing to do with the Association once it was incorporated.

As federal parliament prepared for question time, Coalition frontbencher Christopher Pyne called for the Prime Minister’s resignation, saying her position has become ’’entirely untenable’’.

He said that without Gillard’s letter to Western Australian authorities, the association Mr Wilson later used to siphon funds would never have been registered as a legal entity.

The letter in question has not been found but was alluded to in Gillard’s exit interview from the law firm Slater & Gordon.

''If the Prime Minister had any respect for the Parliament, for the Australian public, for the Labor caucus, she would resign as Prime Minister today and allow the Labor Party to select a new leader... to move on and put this sordid mess behind it,'' Pyne said.

Bishop, who has been leading the Coalition’s pursuit of Gillard over the AWU affair, said the new interview evidence was "devastating for the Prime Minister’s credibility".

"It proves that had she not written to the Commissioner for Corporate Affairs ... it would never have been registered and the misuse of hundreds of thousands of dollars would never have occurred," she told Fairfax Radio on Thursday morning.

Bishop said that there were numerous breaches of the law, such as misleading the Commissioner for Corporate Affairs, that the Coalition would be exploring "over the next little while".